Introduction

Societal and cultural changes over the past decades are considered to be major contributors to the rising obesity epidemic (1). For many people, the subtle decline in daily physical activity along with eating patterns that allow increased caloric intake have resulted in weight gain and development of overweight or obesity. Currently, over 60% of American adults are overweight or obese, whereas 15% of adolescents are considered at risk for overweight (2). Perhaps not surprisingly, the same factors that have led to human obesity underlie the growing prevalence of obesity among companion pets. By the latest estimate, one-quarter of dogs and cats are considered obese (3). Moreover, overweight and obesity are associated with impaired health in both species. To combat this problem, both public health professionals and veterinarians have endorsed a proactive approach that includes adoption of healthy changes in diet and physical activity (4, 5). Creative and fresh ideas are needed to address these rising obesity rates. Because obesity in both species shares common causes and treatment recommendations, would it be beneficial to join forces–people and pets (PP)¹ –to treat the duel obesity epidemic?

There a multiple reasons to support a combined human-pet program to address obesity. The beneficial impact of companion animals on the physical, social, and psychological health of people is well documented (6). This has been particularly studied among patients with cardiovascular disease (7, 8, 9), aging and dementia (10, 11), and those with ambulatory disabilities (12). The positive effect of health and well-being resulting from the interactions with a pet has been called the human-companion animal bond (13).

The other important role that pets play in human health is social support. Past studies conducted among communities and obesity programs have repeatedly shown that social support is one of the most powerful predictors of adoption and maintenance of behavior change (14). This is primarily based on the social learning theory that emphasizes mutual influence between the individual and the environment (15, 16). In a study of nearly 20,000 respondents who participated in the National Health and Nutrition Examination Survey III, social relationships were significant predictors for engagement in five lifestyle and preventive health behaviors related to cardiovascular disease: cigarette smoking, participating in physical activity, consuming fruits and vegetables, having blood pressure checked, and having cholesterol checked (17). The influence of social support on physical activity is particularly strong (18, 19, 20). In a survey of 3342 adults from six countries, the social environment was found to be the strongest independent predictor of being physically active (21). Those who perceive low social support from their personal environment, i.e., family, friends, school, and workplace, were more than twice as likely to be sedentary compared with those who reported high social support from their personal environment. Wing and Jeffery (22) evaluated the importance of social support within a group weight loss program. They found that recruiting participants with a team of three friends and treating them with a strong social support intervention decreased the number of dropouts and markedly increased the percentage of participants who maintained their weight loss in full over a 6-month follow-up period.

Incorporating household pets in a weight loss program offers a potentially new and practical approach to both human and pet obesity. Companion dogs provide a social function. Animal companions are commonly perceived to be a member of the family and share attributes of the living environment (23). Companion dogs may also provide people with a source of social stimulation that is typically more constant and reliable than friends and coworkers (23). This is particularly important for exercise because the presence of a partner is associated with physical activity (24), and dogs will rarely discourage such behavior. Furthermore, people walking with their dog experience more social contact and longer conversations than when walking alone (13). Dogs may also strengthen engagement in a weight loss program by providing challenge support in the way of encouragement and motivation (25). For many individuals, a helping relationship is a strong incentive for participation and goal setting. Furthermore, pet ownership is widespread—it is currently estimated that 39% of U.S. households have dogs as companion animals, whereas 34% have cats (26). Therefore, the potential influence of pets in providing social support provides a rational framework for studying the possible benefits of pets in aiding weight loss among obese people.

Thus, the purpose of this study was to assess the effectiveness of a combined PP weight loss program where both human participants and companion dogs were obese. This people and pet social support condition was compared with people alone who did not own a companion animal. We hypothesized that dogs would serve as a social support system for exercise, and people walking with their dogs would lose more weight at 1 year than people walking alone. Although not designed as a research question, all dogs were placed on a therapeutic hypocaloric diet as part of the combined PP program.

Research Methods and Procedures

Subjects

A 1-year prospective, controlled trial was conducted at the Wellness Institute at Northwestern Memorial Hospital (Chicago, IL). Overweight and obese adults who owned an obese dog (PP group) or did not own a dog [ people only (PO) group] were recruited in the Chicago area through flyers, newspaper advertisements, and veterinary clinics. After an initial telephone screen, participants attended an orientation session where the study was explained, and informed consent was signed. The trial was approved by the institutional review board of Northwestern University and Hill's Institutional Animal Care and Use Committee.

For inclusion in the study, people had to be between 21 and 65 years old, have a BMI > 25 kg/m², be in good general health, and have no limitations to exercise. They had to be weight stable and not taking any medications that would affect their weight for at least 2 months before the start of the study. If they were pet owners (PP group), they had to be concerned about their dog's weight and willing to participate in a weight loss program with their pet. The dogs had to be between 1 and 6 years old, spayed or neutered, and in good general health except for obesity. Obesity, defined as 20% over ideal weight for breed, was determined by body weight and the body condition score (5). The dogs could not be on any weight management program or taking any medications or supplements including vitamins, Prozyme, or herbal treatments for 2 months before the study.

Study Design

The PP and PO groups met separately in small group sessions ranging from six to 12 participants. Groups met weekly for the first 16 weeks (treatment phase), then once a month at months 5, 6, 9, and 12 (maintenance phase). Group sessions were led by a registered dietitian who instructed participants in recognizing and adopting healthy eating, exercise, and coping patterns (27), use of commercial meal replacement products, strategies to reduce total calories and tips on increasing physical activity, and behavioral change techniques. Participants were directed to a target caloric goal of 1400 calories/d and guided to increase physical activity to 20 to 30 minutes on most days of the week. Groups were also given a walking kit handout that contained a variety of facts, suggestions, and community resources.

For the PP group, activities to build cohesiveness between the owners and their pets, self-efficacy concerning confidence and skills regarding dog walking, and motivation were conducted. A veterinarian (K.R.) joined the group for four sessions over the treatment phase to review pet health tips, such as how to prevent injuries, recognize signs of dehydration or exhaustion, identify ways to protect paws, choose pet toys, and identify community pet resources. Owners also met separately with the veterinarian at a kennel on a predetermined schedule for measurements and diet advice for the dogs.

Measures

Participants' height was measured at the start of the trial with a wall-mounted statiometer to the nearest 0.1 cm. Weight was measured at each session to the nearest 0.1 kg using a Scale-Tronix scale (Scale-Tronix, White Plains, NY). Diet and exercise logs were used for participant self-monitoring and data collection. Physical activity was measured by modification of the 7-day physical activity recall (PAR) questionnaire (28). Participants were instructed to record all activity over the previous week that was not considered light, i.e., desk work, standing, light housework, strolling, or stop-and-go walking were not recorded. For all other activity, subjects categorized the activity as moderate, hard, or very hard and recorded total duration. Definitions of the three categories were reviewed. For the PP group, subjects were instructed to designate all dog-related activity (DRA) with an asterisk. For analysis, duration in each category was scored in time blocks of quarter hours, with at least 10 minutes required to be scored (rounded up to 0.25 hours). The PAR was completed at baseline and months 4, 6, and 12. A social support and readiness questionnaire was completed at the same intervals. Using a five-point Likert scale, participants were asked to rate the level at which they agreed or disagreed with a series of social support statements. For the exercise readiness question, subjects were asked to identify with a specific exercise stage of change. Although not used for data collection, subjects were provided a pedometer (Accusplit; http://www.Digi-walker.com) for self-monitoring of steps. At the conclusion of the study, participants were asked to write a narrative regarding their experience that was qualitatively reviewed.

Pets underwent a physical examination and blood testing for complete blood count, serum chemistry profile, and thyroid hormone at baseline and months 6 and 12 to ensure good health. Body weight was obtained at baseline, monthly for the first 4 months, then at months 6, 9, and 12. Body condition score was determined at baseline and months 3, 4, 6, and 12 (5). All dogs were fed a study diet of Hill's Pet Nutrition Prescription Diet r/d until they reached ideal body weight, and then they were fed Prescription Diet w/d for the rest of the study (both foods were provided free from the sponsor).

Data Analysis

Results are expressed as mean and standard deviation group outcomes. Between- and within-group data were analyzed using paired samples Student's t tests. Weight loss results are expressed using three outcome methods: last observation carried forward (LOCF); intention-to-treat, where subjects are presumed to gain weight after dropping out back to baseline weight by 12 months, and completers' analysis. Physical activity data are presented using LOCF. The social support and readiness questionnaire was analyzed using ² analysis. Dog responses were evaluated using ANOVA, with the initial body weight or body condition score used as a covariant and treatment as an independent variable (29). Statistical significance is defined as p < 0.05. Narrative answers were written by all participants who completed the study in response to the question: "Please describe the role that others (friends, coworkers, family, pet, etc.) played in achieving (or not achieving) your goals?" Narrative responses were analyzed using the latent content and constant comparative method (30). For this analysis, two authors and a consultant independently read all responses to identify common themes. Any differences in interpretation were discussed until consensus was reached. Once the themes were developed, the narratives were reexamined for consistency among all three reviewers.

Results

Thirty-six subjects entered the PP group, and 56 entered the PO group. Demographics and descriptive characteristics are presented in Table 1. Despite a nonrandomized design, there were no significant differences among groups. The participants were predominately women, mean age of 45 years old, and moderately obese (BMI, 36 kg/m²). Completion rates were also similar among groups. Eighty-three percent and 75% of the PP and PO subjects, respectively, completed the initial 4-month treatment phase. Twelve-month completion rates were 61% for the PP group and 57% for the PO group. Reasons for drop-outs included self or family illness (n = 7), moved away from the Chicago area (n = 3), scheduling conflict (n = 10), dog became ill (n = 2), pregnancy (n = 1), a PO subject purchased a dog (n = 1), and unknown (n = 14).

Table 1. - Baseline demographics and descriptive characteristics of subjects.

Full table

Weight loss results expressed as LOCF, completers, and intention-to-treat are shown in Table 2. For the PP group, mean (standard deviation) percentage weight losses at 4, 6, and 12 months using LOCF are 4.7% (4.2% ), 5.4% (4.9% ), and 4.7% (4.8% ). Weight losses for the PO group at 4, 6, and 12 months are 5.2% (4.3% ), 6.2% (5.5% ), and 5.2% (6.2% ). Weight loss was statistically different from baseline at each time-point for both groups (p < 0.01), although there were no significant differences among groups at any time-point. Percentage weight losses for subjects who completed the study are greater in both groups. Self-recorded total physical activity by the PAR questionnaire for both groups is displayed in Table 3 and Figure 1. For the PP group, average total physical activity increased 39% over the 1-year study, from 2.8 h/wk at baseline to 3.9 h/wk by month 12 (p < 0.05). For the PO group, average total physical activity increased 87% , from 1.9 to 3.5 h/wk (p < 0.05). Thus, by the end of the study, both groups were engaging in an average of 30 minutes of physical activity per day. Recorded time spent in total, moderate, and designated as DRA is shown in Figures 2and 3. Overall, the majority of physical activity was spent in the moderate category, ranging from 86% to 94% of total activity for the PP group and from 77% to 85% for the PO group. As seen in Figure 2, approximately two-thirds of all activity in the PP group was spent as DRA for all time-points.

Figure 1.

Mean total PAR for the PP group compared with the PO group at baseline and months 4, 6, and 12.

Full figure and legend (62K)

Figure 2.

Mean PAR for the PP group displayed by total activity, moderate activity, and DRA.

Full figure and legend (75K)

Figure 3.

Mean PAR for the PO group displayed by total and moderate activity.

Full figure and legend (61K)

Table 2. - Weight loss.

Full table

Table 3. - Physical activity.

Full table

Attitudes regarding social support and exercise readiness for both groups are seen in Table 4. A minority of participants in both groups received support from family members, friends, or coworkers to make lifestyle changes. In contrast, a majority of subjects felt confident in their ability to participate in physical activity and felt that exercise was important. There were no significant changes seen over the course of the study. On the baseline exercise readiness scores, 66% and 64% of PP and PO participants, respectively, were in the preparation stage of change (results not shown). Both groups showed a significant effect of the intervention on how many participants moved to the action or maintenance phase of physical activity (p < 0.01). The effect was apparent at the first post-test measurement and remained at a consistent level overall three post-test observations. There was no significant difference between the two groups on that measure. The body weight and body condition scores for the dogs are shown in Table 5. There was significant loss in body weight accompanied by significant improvement in body condition score throughout the study (p < 0.05).

Table 4. - Social support and exercise readiness scores^*.

Full table

Table 5. - Dog weight and body condition score, n = 36.

Full table

The major themes noted by latent analysis along with exemplary quotes are shown in Table 6. Of the seven themes associated with social support stemming from people, four were considered positive (cheerleader, buddy, helper, and accountability), and three were considered negative (negative influence, saboteur and inconsistency). No differences were seen between the PP and PO groups regarding social support from people. In contrast, the PP group identified four social support themes related to their dogs, three of which were uniquely identified only with pets. Although the buddy theme was similar to that described for people, the themes of consistent initiator, enjoyment, and parental pride were distinctive to companion dogs.

Table 6. - Major social support themes and exemplary quotes identified by narratives from PP and PO groups.

Full table

Discussion

The PP Exercising Together (PPET) Study is the first trial to show that overweight owners and their overweight companion animals can lose weight together and that companion dogs can serve as social support during the weight loss period. This is an important finding because obesity among PP has reached epidemic proportions. Combining treatment efforts makes sense because the etiology of weight gain is similar in people and their domestic animals, and treatment is more likely to be successful by pairing up. Thus far, the human-companion animal bond has been used therapeutically primarily toward benefiting human health alone. In the PPET study, the focus was on the mutual effectiveness of weight loss in both species.

Two aspects of weight loss were investigated in the trial design: physical activity and social support. These factors were emphasized because companion animals have the unique capacity to support both of these components. Dog walking and playing, which provides physical activity for both PP, is an important potential benefit of dog ownership. Multiple environmental and social factors have been identified as important variables in predicting engagement in physical activity, including modeling, i.e., individuals in home or close friends who exercise regularly; friend and family support; perceived barriers that may prevent exercise, e.g., lack of time, fear of injury, lack of equipment; and neighborhood environment, e.g., safety and ease of exercising, seeing others exercise (31, 32, 33, 34, 35, 36). Steptoe et al. (24) found that patients who reported greater support for lifestyle change from family and friends tended to produce greater increases in physical activity over 4 months. Martin et al. (37) investigated the behavioral and cognitive strategies that would enhance adherence to a 3 d/wk walking/jogging program among sedentary adults. They found that a group/social setting, including instructor feedback and praise during exercise, and flexible goal setting by the individual were important factors. Additional important predictors are motivation and self-efficacy (25).

To enhance the social and physical activity interaction with their companion dogs, owners met with a veterinarian to review safety tips and playtime ideas including pet toys and community resources such as pet-friendly parks. Owners were encouraged to spend as much active time with their pets as possible, with a goal of accumulating 20 to 30 minutes of activity on most days of the week. Participants in both groups were provided with general information on increasing physical activity through activities of daily living and encouraged to use the pedometer to track and monitor progress. Walking was the preferred activity because it could be performed with their pet (PP group), in short bouts (38) and in the multiple locations (39). Both groups recorded an increase in total physical activity by the PAR questionnaire, mostly in the moderate category that corresponds with walking. Participants accumulated 30 minutes of daily activity that is consistent with public health recommendations (40). Our study found that dog owners engaged in more physical activity at baseline, and about two-thirds of reported total activity was obtained with the companion pet. This is consistent with a recent population-based study from Canada where participants were asked to recall their average weekly physical activity over the past month (41). In this study, dog owners spent more time in mild and moderate physical activities and walked an average of 300 min/wk compared with nondog owners who walked an average of 168 min/wk. Although total time spent in physical activity is significantly greater among Canadians than seen in our participants, both studies showed that dog walking contributed to increased walking time. The higher baseline level of activity among the PP group could also explain the smaller increase in total physical activity over 12 months compared with that seen among the PO group.

The narrative essays and major themes identified from the PP and PO participants showed similarities regarding the role that people (family, friends, and coworkers) played in social support. Interestingly, people exhibited both helpful (cheerleader, buddy, helper, and accountability) and unhelpful (negative influence, saboteur, and inconsistent) influences. Companion dogs, on the other hand, provided a buddy along with three uniquely identifiable positive influences: consistent initiator and enjoyment (both exercise related) and parental pride. These influences emerged as considerable sources of social support regarding motivation and encouragement. Our data suggest that companion dogs can serve as a social support system, in addition to other well-described sources, for engagement in physical activity and participation in a weight loss program.

Mean weight loss at 12 months in the PP and PO groups by all analyses was not statistically different among groups. This was a surprising finding because the second hypothesis of the study was that the PP group would lose more weight than the PO group. The social support questionnaire suggested that despite participation in a 12-month weight loss program, participants in both groups did not perceive an increase in help from family and friends to support their effort. Nonetheless, the majority of subjects increased their stage of change to an active participant. This suggests that PO subjects increased activity based on the support that existed at the start of the study and based on counseling provided during the study. Whether pet owners will be more successful in maintaining their weight loss after 1 year based on the human-companion animal bond compared with subjects in the PO group is not known. The percentage of weight loss is consistent with the trial design that emphasized physical activity and social support (42). A 5% weight loss has been found to be beneficial and leads to improvement in cardiovascular risk factors (43). For the dogs, the significant loss of weight and improvement in body composition during the study shows that losing weight and keeping it off is achievable. Excessive deposition of body fat is detrimental in dogs and humans. The significant weight loss shown in the dogs would be expected to improve their health, longevity, and quality of life.

A limitation of the study is the small number of participants enrolled into the PP group. Despite significant recruitment efforts in veterinary offices, veterinarians were reluctant to refer owners and their pets in fear of offending clients. This factor highlights the discomfort and potential stigma that still exists in broaching the subject of overweight and obesity. Another limitation is the relatively high drop-out rate at 12 months. This is consistent with many other diet and pharmacological obesity trials published in the medical literature. We also cannot rule out bias among groups because pet owners may have different characteristics than nonpet owners. We do not have detailed data about the type and extent of exercise that the participants did before entering the study that may have explained, in part, the increased baseline activity level among the PP group. The walking characteristics among groups was also not assessed, i.e., the PP group may have stopped and started more often compared with continuous walking by the PO group. This may have contributed to less total weight loss among the PP subjects.

In conclusion, the PPET study is the first trial to demonstrate the effectiveness of a combined PP weight loss program. Both people and their pets successfully lost weight. If an individual owns a dog, particularly one that is overweight, one should make the most of the dog in an exercise and weight loss program.

Notes

¹ Nonstandard abbreviations: PP, people and pets; PO, people only; PAR, physical activity recall; DRA, dog-related activity; LOCF, last observation carried forward; PPET, People and Pets Exercising Together.

References

1. Weinsier, R. L., Hunter, G. R., Heini, A. F., Goran, M. I., Sell, S. M. (1998) The etiology of obesity: relative contribution of metabolic factors, diet, and physical activity. Am J Med. 105: 145–150. | Article | PubMed | ISI | ChemPort |
2. Hedley, A. A., Ogden, C. L., Johnson, C. L., Carroll, M. D., Curtin, L. R., Flegal, K. M. (2004) Prevalence of overweight and obesity among US children, adolescents, and adults, 1999–2002. JAMA 291: 2847–2850. | Article | PubMed | ISI | ChemPort |
3. Subcommittee on Dog and Cat Nutrition, Committee on Animal Nutrition, National Research Council, National Academy of Sciences Nutrient Requirements of Dogs and Cats http://nap.edu/catalog/10668.html (Accessed May 20, 2006).
4. U.S. Department of Health and Human Services (2001) The Surgeon General's Call to Action to Prevent and Decrease Overweight and Obesity U.S. Department of Health and Human Services, Public Health Service, Office of the Surgeon General Rockville, MD.
5. Hand, M. S. Thatcher, CD Remillard, R. L. Roudebush, P. eds. (2000) Small Animal Clinical Nutrition IV Walsworth Publishing Company Marceline, MO.
6. Fine, A. eds. (2000) The Handbook on Animal Assisted Therapy Academic Press San Diego, CA.
7. Friedman, E., Katcher, A. H., Lynch, J. J., Thomas, S. A. (1980) Animal companions and one-year survival of patients after discharge from a coronary unit. Public Health Rep. 95: 307–312.
8. Anderson, W., Reid, P., Jennings, G. L. (1992) Pet ownership, and risk factors for cardiovascular disease. Med J Aust. 157: 298–301.
9. Friedman, E., Thomas, S. A. (1995) Pet ownership, social support, and one-year survival after acute myocardial infarction in the Cardiac Arrhythmia Suppression Trial (CAST). Am J Cardiol. 76: 1213–1217.
10. Churchill, M., Safaoui, J., McCabe, B., Baun, M. (1999) Using a therapy dog to alleviate the agitation and desocialization of people with Alzheimer's disease. J Psych Nursing 37: 16–22.
11. Raina, P., Waltner-Toews, B., Bonnett, B., Woodward, C., Abernathy, T. (1999) Influence of companion animals on the physical and psychological health of older people. J Am Geriatr Soc. 47: 323–329.
12. Allen, K. M., Blascovich, J. (1996) The value of service dogs for people with severe ambulatory disabilities: a randomized controlled trial. JAMA 275: 1001–1006.
13. Beck, A. M., Meyers, M. (1996) Health enhancement and companion animal ownership. Annu Rev Health 17: 247–257.
14. Cohen, S. (2004) Social relationships and health. Am Psychol. 59: 676–684. | Article | PubMed | ISI |
15. Bandura, A. (1986) Social Foundations of Thought and Action Prentice-Hall Englewood Cliffs, NJ.
16. Booth, S. L., Sallis, J. F., Ritenbaugh, C., et al (2001) Environmental and societal factors affect food choice and physical activity: rationale, influences, and leverage points. Nutr Rev. 59: S21–S39. | PubMed | ISI | ChemPort |
17. Ford, E. S., Ahluwalia, I. B., Galuska, D. A. (2000) Social relationships and cardiovascular disease risk factors: findings from the Third National Health and Nutrition Examination Survey. Prev Med. 30: 83–92. | Article | PubMed |
18. Estabrooks, P. A. (2000) Sustaining exercise participation through group cohesion. Exerc Sports Sci Rev. 28: 63–67.
19. Janisse, H. C., Nedd, D., Escamilla, S., Nies, M. A. (2004) Physical activity, social support, and family structure as determinants of mood among European-American and African-American women. Women Health 39: 101–116.
20. Wolfe, W. A. (2004) A review: maximizing social-support-a neglected strategy for improving weight management with African-American women. Ethn Dis. 14: 212–218.
21. Stahl, T., Rutten, A., Nutbeam, D., et al (2001) The importance of the social environment for physically active lifestyle: results from an international study. Soc Sci Med. 52: 1–10. | Article | PubMed |
22. Wing, R. R., Jeffery, R. W. (1999) Benefits of recruiting participants with friends an increasing social support of weight loss and maintenance. J Consult Clin Psychol. 67: 132–138. | Article | PubMed | ChemPort |
23. National Institutes of Health OMAR Workshop The Health Benefits of Pets: NIH Technology Assess Statement Online: September 10–11, 1987 http://consensus.nih.gov/1987/1987HealthBenefitsPetsa003html.htm (Accessed September 9, 2006).
24. Steptoe, A., Rink, E., Kerry, S. (2000) Psychosocial predictors of change in physical activity in overweight sedentary adults following counseling in primary care. Prev Med. 31: 183–194.
25. Biddle, S. J. H., Fox, K. R. (1998) Motivation for physical activity and weight management. Int J Obesity 22: (Suppl 2), S39–S47.
26. The Humane Society of the United States U.S. Pet Ownership Statistics http://www.hsus.org/pets/ (Accessed May 20, 2006).
27. Kushner, R. F., Kushner, N. (2004) Dr. Kushner's Personality Type Diet St Martin's Griffin Press New York.
28. (1997) Seven-day physical activity recall. Med Sci Sports Exerc. 29: S89–S103.(suppl).
29. SAS Institute (1999) SAS/STAT User's Guide, Version 8 SAS Institute Inc Cary, NC.
30. Strauss, , Anselm, L., Corbin, J. (1998) Basics of Qualitative Research: Techniques and Procedures for Developing Grounded Theory 2nd ed. Sage Thousand Oaks, CA.
31. Sallis, J. J., Haskell, W. L., Fortman, S. P., Vranizan, K. M., Barr Taylor, C., Solomon, D. S. (1986) Predictors of adoption and maintenance of physical activity in community sample. Prev Med. 15: 331–341. | PubMed |
32. Sallis, J. F., Grossman, R. M., Pinski, R. B., Patterson, T. L., Nader, P. R. (1987) The development of scales to measure social support for diet and exercise behaviors. Prev Med. 16: 825–836. | Article | PubMed | ISI | ChemPort |
33. Sallis, J. F., Hovell, M. F., Hofstetter, C. R., et al (1989) A multivariate study of determination of vigorous exercise is a community sample. Prev Med. 18: 20–34.
34. Sallis, J. F., Hovell, M. F., Hofstetter, C. R. (1992) Predictors of adoption and maintenance of vigorous physical activity in men and women. Prev Med. 21: 237–251.
35. Eyler, A. A., Brownson, R. C., King, A. C., Brown, C., Sallis, J. F. (1999) Physical activity social support and middle- and older-aged minority women: results from a US survey. Soc Sci Med. 49: 781–789.
36. Addy, C. L., Wilson, D. K., Ainsworth, B. E., Sharpe, P., Kimsey, D. (2004) Associations of perceived social and physical environmental supports with physical activity and walking behavior. Am J Public Health 94: 440–443. | PubMed |
37. Martin, J. E., Dubbert, P. M., Katell, A. D., et al (1984) Behavioral control of exercise in sedentary adults: studies 1 through 6. J Consult Clin Psychol. 52: 795–811.
38. Coleman, K. J., Raynor, H. R., Mueller, D. M., Cerny, F. J., Dorn, J. M., Epstein, L. H. (1999) Providing sedentary adults with choices for their walking goals. Prev Med. 28: 510–519.
39. Eyler, A. A., Brownson, R. C., Bacak, S. J., Housemann, R. A. (2003) The epidemiology of walking for physical activity in the United States. Med Sci Sports Exerc. 35: 1529–1536.
40. Pate, R. R., Pratt, M., Blair, S. N., et al (1995) Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 273: 402–407. | Article | PubMed | ISI | ChemPort |
41. Brown, S. G., Rhodes, R. E. (2006) Relationship among dog ownership and leisure-time walking in western Canadian adults. Am J Prev Med. 30: 131–136.
42. Wing, R. R. (1999) Physical activity in the treatment of the adulthood overweight and obesity: current evidence and research issues. Med Sci Sports Exerc. 31: S547–S552.(suppl): | Article | PubMed | ISI | ChemPort |
43. National Heart, Lung, and Blood Institute (NHLBI) (1998) Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults: the evidence report. Obes Res. 6 (Suppl 2), 51S–210S. | PubMed | ISI |

Acknowledgments

We acknowledge Julie Freidman and Kenzie A. Cameron for statistical and methodological assistance and Amy Baltes and Vicki Shanta-Retelny for assistance in conducting groups. This work was supported by Hill's Pet Nutrition (Topeka, KS).